Plant & Animal Genomes XIII Conference

January 15-19, 2005
Town & Country Convention Center
San Diego, CA

Heading Date 5, A Putative Subunit Of The CCAAT-Box-Binding Transcription Factor, Plays An Important Role In Photoperidic Flowering In Rice

Utako Yamanouchi¹ , Yasunori Nonoue² , Motoyuki Ashikari¹ , Hongxuan Lin¹ , Takuji Sasaki¹ , Takeshi Izawa¹ , Masahiro Yano¹

¹  National Institute of Agrobiological Sciences, Kannondai, Tsukuba, Ibaraki 305-8602, Japan

²  Institute of the Society for Techno-Innovation of Agriculture, Forestry and Fisheries, Kamiyokoba, Tsukuba, Ibaraki 305-0854, Japan

Fifteen quantitative trait loci (QTLs) for flowering time were mapped in a cross between a japonica cultivar, Nipponbare, and an indica cultivar, Kasalath, in rice. A QTL, Heading date 5 (Hd5), on the short arm of chromosome 8 was found to be involved in inhibition of flowering under long-day conditions, but no effect was observed under short-day conditions. Epistatic interaction was observed between Hd5 and Hd1, a major QTL for photoperiodic flowering and an ortholog of Arabidopsis CONSTANS, by analysis of the F₂ population derived from a cross between nearly a isogenic line of Hd5, NIL(Hd5), and NIL(Hd1). High-resolution linkage analysis of 2308 plants defined a genomic region of 4.3 kb as a candidate for Hd5. We found one predicted gene that showed high homology to a CCAAT-box-binding transcription factor subunit. Transgenic analysis verified the function of the candidate gene for Hd5; days-to-heading was increased in Nipponbare plants with the Kasalath allele transgene under long-day conditions. We also found a naturally occurring nucleotide variation, resulting in loss of function, in Hd5 in an extremely early heading cultivar, Hayamasari, which showed complete loss of photoperiodic response of flowering. RT-PCR assay revealed no effect of Hd5 on the mRNA level of Hd1, and vice-versa. However, Hd5 suppressed the mRNA level of Ehd1 (Early heading date 1), one of the recently cloned flowering time QTLs, and Hd3a, an ortholog of Arabidopsis FT. These results suggest that Hd5 plays an important role in transcriptional activation upstream of Ehd1.